blkio: Add more debug-only per-cgroup stats

1) group_wait_time - This is the amount of time the cgroup had to wait to get a
  timeslice for one of its queues from when it became busy, i.e., went from 0
  to 1 request queued. This is different from the io_wait_time which is the
  cumulative total of the amount of time spent by each IO in that cgroup waiting
  in the scheduler queue. This stat is a great way to find out any jobs in the
  fleet that are being starved or waiting for longer than what is expected (due
  to an IO controller bug or any other issue).
2) empty_time - This is the amount of time a cgroup spends w/o any pending
   requests. This stat is useful when a job does not seem to be able to use its
   assigned disk share by helping check if that is happening due to an IO
   controller bug or because the job is not submitting enough IOs.
3) idle_time - This is the amount of time spent by the IO scheduler idling
   for a given cgroup in anticipation of a better request than the exising ones
   from other queues/cgroups.

All these stats are recorded using start and stop events. When reading these
stats, we do not add the delta between the current time and the last start time
if we're between the start and stop events. We avoid doing this to make sure
that these numbers are always monotonically increasing when read. Since we're
using sched_clock() which may use the tsc as its source, it may induce some
inconsistency (due to tsc resync across cpus) if we included the current delta.

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 32 insertions, 18 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 8e0b86a9111a..b6e095c7ef5e 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -886,7 +886,7 @@ static inline unsigned int cfq_cfqq_slice_usage(struct cfq_queue *cfqq)
 }
 
 static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
-                                struct cfq_queue *cfqq)
+                                struct cfq_queue *cfqq, bool forced)
 {
         struct cfq_rb_root *st = &cfqd->grp_service_tree;
         unsigned int used_sl, charge_sl;
@@ -916,6 +916,7 @@ static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
         cfq_log_cfqg(cfqd, cfqg, "served: vt=%llu min_vt=%llu", cfqg->vdisktime,
                                         st->min_vdisktime);
         blkiocg_update_timeslice_used(&cfqg->blkg, used_sl);
+        blkiocg_set_start_empty_time(&cfqg->blkg, forced);
 }
 
 #ifdef CONFIG_CFQ_GROUP_IOSCHED
@@ -1528,6 +1529,12 @@ static int cfq_allow_merge(struct request_queue *q, struct request *rq,
         return cfqq == RQ_CFQQ(rq);
 }
 
+static inline void cfq_del_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+        del_timer(&cfqd->idle_slice_timer);
+        blkiocg_update_idle_time_stats(&cfqq->cfqg->blkg);
+}
+
 static void __cfq_set_active_queue(struct cfq_data *cfqd,
                                    struct cfq_queue *cfqq)
 {
@@ -1547,7 +1554,7 @@ static void __cfq_set_active_queue(struct cfq_data *cfqd,
                 cfq_clear_cfqq_fifo_expire(cfqq);
                 cfq_mark_cfqq_slice_new(cfqq);
 
-                del_timer(&cfqd->idle_slice_timer);
+                cfq_del_timer(cfqd, cfqq);
         }
 
         cfqd->active_queue = cfqq;
@@ -1558,12 +1565,12 @@ static void __cfq_set_active_queue(struct cfq_data *cfqd,
  */
 static void
 __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
-                    bool timed_out)
+                    bool timed_out, bool forced)
 {
         cfq_log_cfqq(cfqd, cfqq, "slice expired t=%d", timed_out);
 
         if (cfq_cfqq_wait_request(cfqq))
-                del_timer(&cfqd->idle_slice_timer);
+                cfq_del_timer(cfqd, cfqq);
 
         cfq_clear_cfqq_wait_request(cfqq);
         cfq_clear_cfqq_wait_busy(cfqq);
@@ -1585,7 +1592,7 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                 cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
         }
 
-        cfq_group_served(cfqd, cfqq->cfqg, cfqq);
+        cfq_group_served(cfqd, cfqq->cfqg, cfqq, forced);
 
         if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
                 cfq_del_cfqq_rr(cfqd, cfqq);
@@ -1604,12 +1611,13 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
         }
 }
 
-static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out)
+static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out,
+                                        bool forced)
 {
         struct cfq_queue *cfqq = cfqd->active_queue;
 
         if (cfqq)
-                __cfq_slice_expired(cfqd, cfqq, timed_out);
+                __cfq_slice_expired(cfqd, cfqq, timed_out, forced);
 }
 
 /*
@@ -1865,6 +1873,7 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
         sl = cfqd->cfq_slice_idle;
 
         mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
+        blkiocg_update_set_idle_time_stats(&cfqq->cfqg->blkg);
         cfq_log_cfqq(cfqd, cfqq, "arm_idle: %lu", sl);
 }
 
@@ -2176,7 +2185,7 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
         }
 
 expire:
-        cfq_slice_expired(cfqd, 0);
+        cfq_slice_expired(cfqd, 0, false);
 new_queue:
         /*
          * Current queue expired. Check if we have to switch to a new
@@ -2202,7 +2211,7 @@ static int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)
         BUG_ON(!list_empty(&cfqq->fifo));
 
         /* By default cfqq is not expired if it is empty. Do it explicitly */
-        __cfq_slice_expired(cfqq->cfqd, cfqq, 0);
+        __cfq_slice_expired(cfqq->cfqd, cfqq, 0, true);
         return dispatched;
 }
 
@@ -2218,7 +2227,7 @@ static int cfq_forced_dispatch(struct cfq_data *cfqd)
         while ((cfqq = cfq_get_next_queue_forced(cfqd)) != NULL)
                 dispatched += __cfq_forced_dispatch_cfqq(cfqq);
 
-        cfq_slice_expired(cfqd, 0);
+        cfq_slice_expired(cfqd, 0, true);
         BUG_ON(cfqd->busy_queues);
 
         cfq_log(cfqd, "forced_dispatch=%d", dispatched);
@@ -2382,10 +2391,15 @@ static int cfq_dispatch_requests(struct request_queue *q, int force)
             cfqq->slice_dispatch >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
             cfq_class_idle(cfqq))) {
                 cfqq->slice_end = jiffies + 1;
-                cfq_slice_expired(cfqd, 0);
+                cfq_slice_expired(cfqd, 0, false);
         }
 
         cfq_log_cfqq(cfqd, cfqq, "dispatched a request");
+        /*
+         * This is needed since we don't exactly match the mod_timer() and
+         * del_timer() calls in CFQ.
+         */
+        blkiocg_update_idle_time_stats(&cfqq->cfqg->blkg);
         return 1;
 }
 
@@ -2413,7 +2427,7 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
         orig_cfqg = cfqq->orig_cfqg;
 
         if (unlikely(cfqd->active_queue == cfqq)) {
-                __cfq_slice_expired(cfqd, cfqq, 0);
+                __cfq_slice_expired(cfqd, cfqq, 0, false);
                 cfq_schedule_dispatch(cfqd);
         }
 
@@ -2514,7 +2528,7 @@ static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
         struct cfq_queue *__cfqq, *next;
 
         if (unlikely(cfqq == cfqd->active_queue)) {
-                __cfq_slice_expired(cfqd, cfqq, 0);
+                __cfq_slice_expired(cfqd, cfqq, 0, false);
                 cfq_schedule_dispatch(cfqd);
         }
 
@@ -3143,7 +3157,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
 static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 {
         cfq_log_cfqq(cfqd, cfqq, "preempt");
-        cfq_slice_expired(cfqd, 1);
+        cfq_slice_expired(cfqd, 1, false);
 
         /*
          * Put the new queue at the front of the of the current list,
@@ -3191,7 +3205,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                 if (cfq_cfqq_wait_request(cfqq)) {
                         if (blk_rq_bytes(rq) > PAGE_CACHE_SIZE ||
                             cfqd->busy_queues > 1) {
-                                del_timer(&cfqd->idle_slice_timer);
+                                cfq_del_timer(cfqd, cfqq);
                                 cfq_clear_cfqq_wait_request(cfqq);
                                 __blk_run_queue(cfqd->queue);
                         } else
@@ -3352,7 +3366,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
                  * - when there is a close cooperator
                  */
                 if (cfq_slice_used(cfqq) || cfq_class_idle(cfqq))
-                        cfq_slice_expired(cfqd, 1);
+                        cfq_slice_expired(cfqd, 1, false);
                 else if (sync && cfqq_empty &&
                          !cfq_close_cooperator(cfqd, cfqq)) {
                         cfqd->noidle_tree_requires_idle |= !rq_noidle(rq);
@@ -3612,7 +3626,7 @@ static void cfq_idle_slice_timer(unsigned long data)
                 cfq_clear_cfqq_deep(cfqq);
         }
 expire:
-        cfq_slice_expired(cfqd, timed_out);
+        cfq_slice_expired(cfqd, timed_out, false);
 out_kick:
         cfq_schedule_dispatch(cfqd);
 out_cont:
@@ -3655,7 +3669,7 @@ static void cfq_exit_queue(struct elevator_queue *e)
         spin_lock_irq(q->queue_lock);
 
         if (cfqd->active_queue)
-                __cfq_slice_expired(cfqd, cfqd->active_queue, 0);
+                __cfq_slice_expired(cfqd, cfqd->active_queue, 0, false);
 
         while (!list_empty(&cfqd->cic_list)) {
                 struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,